Diabetes is a life-long disease characterized by chronic hyperglycemia. Type 1 diabetes is caused by autoimmune destruction of insulin producing β-cells in the pancreas and its treatment is solely dependent on insulin administration. Islet transplantation from cadaveric donors is a promising therapy for type 1 diabetes; however, due to difficulties of obtaining transplantable islets from cadaveric pancreas, alternative cell sources for the generation of insulin expressing β-cells are expected.
Human pluripotent stem cells, e.g., human embryonic stem (hES) cells and human induced pluripotent stem (hiPS) cells, possess the capacity for unlimited replication and the potential to differentiate into all major somatic cell lineages. Therefore, it is believed that those cells are a potential material for generating insulin-producing, pancreatic β-cells. Further, those cells have great potential for use in cell-based therapy and drug discovery. Many studies reported the generation of pancreatic endocrine cells from human ES/iPS cells in various in vitro feeder-cell culture systems (Non-Patent Documents Nos. 1-4) or feeder-free culture systems (Non-Patent Documents Nos. 5-9). Studies on the differentiation of human ES or iPS cells into endodermal or pancreatic cell lineages have shown that activin, fibroblast growth factor (FGF), stimulation with retinoic acid (RA), and inhibition of signaling of hedgehog, bone morphogenetic protein (BMP) and transforming growth factor (TGF)-β promote the differentiation into endodermal or pancreatic lineages (Non-Patent Documents Nos. 1-5 and 10). Stepwise differentiation protocols have been designed to mimic pancreatic differentiation and to successfully generate insulin-expressing cells from human ES or iPS cells.
However, pancreatic β-like cells generated to date from human ES/iPS cells in vitro are largely polyhormonal and exhibit limited capacity of glucose-stimulated insulin secretion (GSIS), a characteristic of functionally mature β-cells (Non-Patent Documents Nos. 6, 8, 10 and 11; Patent Documents Nos. 1 and 2). Moreover, use of chemically undefined raw materials in the generation of β-cells may cause problems in clinical applications in the future. Therefore, development of a method for generating functional and yet terminally differentiated endocrine cell-type β-cells from human iPS (hiPS) cells in a defined xeno-free culture system has been greatly desired.